Integrated circuits are formed on a semiconductor substrate, which is typically composed of silicon. Such formation of integrated circuits involves sequentially forming or depositing multiple electrically conductive and insulative layers in or on the substrate. Etching processes may then be used to form geometric patterns in the layers or vias for electrical contact between the layers. Etching processes include “wet” etching, in which one or more chemical reagents are brought into direct contact with the substrate, and “dry” etching, such as plasma etching.
Various types of plasma etching processes are known in the art, including plasma etching, reactive ion (RI) etching and reactive ion beam etching. In each of these plasma processes, a gas is first introduced into a reaction chamber and then plasma is generated from the gas. This is accomplished by dissociation of the gas into ions, free radicals and electrons by using an RF (radio frequency) generator, which includes one or more electrodes. The electrodes are accelerated in an electric field generated by the electrodes, and the energized electrons strike gas molecules to form additional ions, free radicals and electrons, which strike additional gas molecules, and the plasma eventually becomes self-sustaining. The ions, free radicals and electrons in the plasma react chemically with the layer material on the semiconductor wafer to form residual products which leave the wafer surface and thus, etch the material from the wafer.
Referring to the schematic of FIG. 1, a conventional plasma etching system, such as an Mxp+Super-E etcher available from Applied Materials, Inc., is generally indicated by reference numeral 10. The etching system 10 includes a reaction chamber 12 having a typically grounded chamber wall 14. An electrode, such as a planar coil electrode 16, is positioned adjacent to a dielectric plate 18 which separates the electrode 16 from the interior of the reaction chamber 12. Plasma-generating source gases are provided by a gas supply (not shown) and flow into the reaction chamber 12 through openings 18a in the gas distribution plate 18. Volatile reaction products and unreacted plasma species are removed from the reaction chamber 12 by a gas removal mechanism, such as a vacuum pump 24 through a throttle valve 26.
Electrode power such as a high voltage signal is applied to the electrode 16 to ignite and sustain a plasma in the reaction chamber 12. Ignition of a plasma in the reaction chamber 12 is accomplished primarily by electrostatic coupling of the electrode 16 with the source gases, due to the large-magnitude voltage applied to the electrode 16 and the resulting electric fields produced in the reaction chamber 12. Once ignited, the plasma is sustained by electromagnetic induction effects associated with time-varying magnetic fields produced by the alternating currents applied to the electrode 16. The plasma may become self-sustaining in the reaction chamber 12 due to the generation of energized electrons from the source gases and striking of the electrons with gas molecules to generate additional ions, free radicals and electrons. A semiconductor wafer 34 is positioned in the reaction chamber 12 and is supported by a water platform or ESC (electrostatic chuck) 36. The ESC 36 is typically electrically-biased to provide ion energies that are independent of the RF voltage applied to the electrode 16 and that impact the wafer 34.
Typically, the voltage varies as a function of position along the coil electrode 16, with relatively higher-amplitude voltages occurring at certain positions along the electrode 16 and relatively lower-amplitude voltages occurring at other positions along the electrode 16. A relatively large electric field strength is required to ignite plasmas in the reaction chamber 12. Accordingly, to create such an electric field it is desirable to provide the relatively higher-amplitude voltages at locations along the electrode 16 which are close to the grounded chamber wall 14.
As discussed above, plasma includes high-energy ions, free radicals and electrons which react chemically with the surface material of the semiconductor wafer to form reaction produces that leave the wafer surface, thereby etching a geometrical pattern or a via in a wafer layer. Plasma intensity depends on the type of etchant gas or gases used, as well as the etchant gas pressure and temperature and the radio frequency generated at the electrode 16. If any of these factors changes during the process, the plasma intensity may increase or decrease with respect to the plasma intensity level required for optimum etching in a particular application. Decreased plasma intensity results in decreased, and thus incomplete, etching. Increased plasma intensity, on the other hand, can cause overetching and plasma-induced damage of the wafers. Plasma-induced damage includes trapped interface charges, material defects migration into bulk materials, and contamination caused by the deposition of etch products on material surfaces. Etch damage induced by reactive plasma can alter the qualities of sensitive IC components such as Schottky diodes, the rectifying capability of which can be reduced considerably. Heavy-polymer deposition during oxide contact hole etching may cause high-contact resistance.
The gas distribution plate 18 illustrated in FIG. 1 may serve multiple purposes and have multiple structural features, as is well known in the art. For example, the gas distribution plate 18 may include features in addition to the openings 18a for introducing the source gases into the reaction chamber 12, as well as those structures associated with physically separating the electrode 16 from the interior of the chamber 12. The openings 18a typically have a diameter of about 0.5 mm, and the gas distribution plate 18 is constructed of quartz.
One of the limitations inherent in the quartz gas distribution plate 18 is that plasma may damage or corrode the gas distribution plate 18 during plasma processes carried out in the chamber 12. Furthermore, over prolonged periods of use the quartz gas distribution plate 18 deteriorates and generates particles which have the potential to contaminate a wafer 34 processed in the reaction chamber 12. Accordingly, a new and improved gas distribution plate which is characterized by enhanced durability and resistance to damage and deterioration is needed for a reaction chamber.
According to the present invention, an anodized aluminum gas distribution plate is provided which is durable and resistant to plasma-induced damage and deterioration. Anodizing is a type of electrolysis by which a protective oxide coating is formed on a metal. Anodizing may serve several purposes, including forming a tough coating on a metal as well as imparting electrical insulation and corrosion resistance to the metal. Anodized aluminum and magnesium are commonly used in airplanes, trains, ships and buildings.
Anodizing processes are carried out in an electrolyte solution, in which the metal to be anodized acts as an anode or positive pole of the cell. Negatively charged oxide ions pass through the electrolyte solution and oxidize the surface of the metal. Aluminum is typically anodized in a sulfuric acid electrolyte solution, whereas magnesium is often anodized in a dichromate electrolyte solution. The thickness of the anodized coating is a function of the magnitude of the electric current which is passed through the solution. The anodized metal surface may be subjected to special treatments to give the metal a porous layer that can absorb dyes which are incapable of being rubbed or scratched off the surface.
An object of the present invention is to provide a new and improved gas distribution plate for a process chamber.
Another object of the present invention is to provide a new and improved gas distribution plate which is characterized by longevity and durability.
Still another object of the present invention is to provide a new and improved gas distribution plate which is suitable for use in etch chambers used in the fabrication of integrated circuits on semiconductor wafers.
Yet another object of the present invention is to provide a new and improved, anodized aluminum gas distribution plate.
A still further object of the present invention is to provide a method of fabricating an anodized aluminum gas distribution plate.